Method of forming a power semiconductor device and power semiconductor device

Abstract

A method of forming a power semiconductor device comprises forming a first semiconductor layer of a first conductivity type extending across the power semiconductor device; forming an epitaxial layer of the first conductivity type over the first semiconductor layer, the epitaxial layer having a doping concentration that increases from a first surface of the epitaxial layer towards the first semiconductor layer; forming a body region of a second conductivity type in the epitaxial layer extending from the first surface of the epitaxial layer into the epitaxial layer, wherein a junction between the body region and the epitaxial layer is at or substantially adjacent to a region of the epitaxial layer having a maximum doping concentration; and forming a gate region such that the gate region is adjacent at least a portion of the body region. In operation of the semiconductor device, the portion of the body region adjacent the gate region functions as a channel region of the semiconductor device.

The invention claimed is: 
     
       1. A method of forming a power semiconductor device comprising:
 forming a first semiconductor layer of a first conductivity type extending across the power semiconductor device; 
 forming an epitaxial layer of the first conductivity type over the first semiconductor layer, the epitaxial layer having a doping concentration that increases from a first surface of the epitaxial layer towards the first semiconductor layer to provide a first region adjacent to the first surface having a doping concentration lower than a second region adjacent to the first semiconductor layer; 
 forming a body region of a second conductivity type in the epitaxial layer extending from the first surface of the epitaxial layer into the epitaxial layer, wherein a PN junction between the body region and the epitaxial layer extends through the first region and into the second region so that a maximum depth of the PN junction is at or just adjacent to a region of the epitaxial layer having a maximum doping concentration; and 
 forming a gate region such that the gate region is adjacent at least a portion of the body region, wherein in operation of the semiconductor device the portion of the body region adjacent the gate region functions as a channel region of the semiconductor device. 
 
     
     
       2. The method according to  claim 1 , wherein forming an epitaxial layer comprises forming a blanket epitaxial layer extending across substantially all of the first semiconductor layer. 
     
     
       3. The method according to  claim 1 , wherein the first semiconductor layer is an epitaxial layer and wherein the steps of forming the first semiconductor layer and the epitaxial layer are performed in the same epitaxial apparatus. 
     
     
       4. The method according to  claim 1 , wherein the first semiconductor layer has a first doping concentration of the first conductivity type and wherein the doping concentration across the epitaxial layer is greater than the first doping concentration. 
     
     
       5. The method according to  claim 1 , wherein the step of forming the gate region comprises forming the gate region over the first surface of the epitaxial layer such that the gate region extends over at least a portion of the body region and at least a portion of the epitaxial layer. 
     
     
       6. The method according to  claim 1 , further comprising forming a current electrode region of the first conductivity type in the body region extending from the first surface into the body region. 
     
     
       7. The method according to  claim 1 , wherein forming a first semiconductor layer comprises forming the first semiconductor layer over a semiconductor substrate. 
     
     
       8. The method according to  claim 7 , wherein the semiconductor substrate is of the second conductivity type and has a first surface and a second surface wherein the first semiconductor layer is formed over the first surface of the semiconductor substrate and wherein the method further comprises forming a current electrode over the second surface of the semiconductor substrate. 
     
     
       9. The method according to  claim 1 , wherein the power semiconductor device comprises an active area and a termination area surrounding the active area, wherein the first semiconductor layer, and the epitaxial layer extend across the active area and termination area and wherein the body region and gate region are formed in the active area, the method further comprising forming at least one protection structure in the termination area to compensate for the doping concentration of the epitaxial layer. 
     
     
       10. The method according to  claim 9 , wherein the protection structure comprises at least one of:
 a termination region of the second conductivity type in the termination area, the at least one termination region extending from the first surface of the epitaxial layer into the epitaxial layer and 
 a termination region of the first conductivity type in the epitaxial layer adjacent the first surface of the epitaxial layer. 
 
     
     
       11. A power semiconductor device comprising:
 a first semiconductor layer of a first conductivity type extending across the power semiconductor device; 
 an epitaxial layer of the first conductivity type formed over the first semiconductor layer, the epitaxial layer having a doping concentration that increases from a first surface of the epitaxial layer towards the first semiconductor layer to provide a first region adjacent to the first surface having a doping concentration lower than a second region adjacent to the first semiconductor layer; 
 a body region of a second conductivity type formed in the epitaxial layer extending from the first surface of the epitaxial layer into the epitaxial layer, wherein a PN junction between the body region and the epitaxial layer extends through the first region and into the second region so that a maximum depth of the PN junction is at or just adjacent to a region of the epitaxial layer having a maximum doping concentration; and 
 a gate region adjacent at least a portion of the body region, wherein in operation of the semiconductor device the portion of the body region adjacent the gate region functions as a channel region of the semiconductor device. 
 
     
     
       12. The power semiconductor device according to  claim 11 , wherein the epitaxial layer is a blanket epitaxial layer extending across substantially all of the first semiconductor layer. 
     
     
       13. The power semiconductor device according to  claim 11 , wherein the first semiconductor layer has a first doping concentration of the first conductivity type and wherein the doping concentration across the epitaxial layer is greater than the first doping concentration. 
     
     
       14. The power semiconductor device according to  claim 11 , wherein the gate region is formed over the first surface of the epitaxial layer such that the gate region extends over at least a portion of the body region and at least a portion of the epitaxial layer. 
     
     
       15. The power semiconductor device according to  claim 11 , further comprising a current electrode region of the first conductivity type formed in the body region extending from the first surface into the body region. 
     
     
       16. The power semiconductor device according to  claim 11 , further comprising a semiconductor substrate, wherein the first semiconductor layer is formed over the semiconductor substrate. 
     
     
       17. The power semiconductor device according to  claim 16 , wherein the semiconductor substrate is of the second conductivity type and has a first surface and a second surface wherein the first semiconductor layer is formed over the first surface of the semiconductor substrate and the semiconductor device further comprises a current electrode formed over the second surface of the semiconductor substrate. 
     
     
       18. The power semiconductor device according to  claim 11 , wherein the power semiconductor device comprises an active area and a termination area surrounding the active area, wherein the first semiconductor layer, and the epitaxial layer extend across the active area and termination area and wherein the body region and gate region are formed in the active area, the semiconductor device further comprising at least one protection structure formed in the termination area to compensate for the doping concentration of the epitaxial layer. 
     
     
       19. The power semiconductor device according to  claim 18 , wherein the protection structure comprises at least one of:
 a termination region of the second conductivity type in the termination area, the at least one termination region extending from the first surface of the epitaxial layer into the epitaxial layer; and 
 a termination region of the first conductivity type in the epitaxial layer adjacent the first surface of the epitaxial layer. 
 
     
     
       20. The method according to  claim 1  wherein the first region and the second region of the epitaxial layer are formed during one epitaxial process, and wherein a concentration of a dopant of the first type is varied during the epitaxial process.